Digital communications networks are used to interconnect digital systems or "hosts" so that the hosts may exchange information in an efficient manner. A common type of digital communications network is the Local Area Network (LAN), and a common type of LAN is commonly known as "Ethernet". A typical example of an Ethernet network includes a multiplicity of personal computers (PCs) and a laser printer interconnected by coaxial cable or twisted-pair wire. PCs coupled to the Ethernet network may share the laser printer or exchange electronic mail with one another. LANs typically have a physically limited area of service, and Metropolitan Area Networks (MANs) and Wide Area Networks (WANs) are used to interconnect more remote systems.
As an enterprise such as a business organization grows, so does its networking needs. A common method for meeting increased networking demands is to interconnect two or more networks. This method is called "internetworking," and internetworking devices such as repeaters (also known as "hubs" and "connectors"), bridges, and routers (also known as "gateways") are used to accomplish this task.
Repeaters, as their name implies, are used to "repeat" signals such that the physical size of a LAN may be increased. Bridges are used to interconnect LANs of the same type in a manner that results in the interconnected LANs operating as a single LAN.
Routers are internetworking devices that are used to interconnect distinct networks, however defined, to allow the exchange of information between the hosts of the interconnected networks. Routers may be used to interconnect multiple networks of the same or different network type. For example, a router may be used to interconnect two Ethernet LANs with a Token Ring LAN. Furthermore, routers may be used to interconnect physically distinct networks, logically distinct networks defined within a single physical network (e.g. virtual networks or emulated LANs), or a combination of physically and logically distinct networks.
Typically, each distinct network is specified by a unique network address and is connected to a router via its own physical interface. For example, FIG. 1 shows a router 100 that includes ports 101-107, each of which is coupled to a different network. A number of physically distinct networks are shown and include a network 110 having logical networks A and B defined therein, a Fiber Distributed Data Interface (FDDI) network 115, an Ethernet network 120, an Asynchronous Transfer Mode (ATM) network 125, a Wide Area Network (WAN) 130, and a Token Ring Network 135.
The number of ports that may be provided for a single router is limited by many practical considerations. Therefore, it would be desirable for providing a mechanism that allows for a reduction in the number of ports required to interconnect a multiplicity of distinct networks. In this manner, a single router may be used to interconnect more distinct networks than is practicable using prior art schemes.